I received a new cam recently for an engine my son & I are rebuilding for the 67 GTO 400 4 spd with a mild extreme energy Comp Cam. In reading the instruction/install tip sheet I noticed a comment about break in... Comp does not recommend using synthetic oil on break in. I went by a performance engine machine shop which has a very good reputation and the machinist expressed that he agreed and uses regular oil on break in because the machined metal surfaces have to mate/burnish together and that syn oils are too slippery and interfere with that process. That is the same thing a Chevy dealer mech told me and our 04 GTO'S came with regular oil from GM because the LS1 is a fast rev engine and needs to have enough friction between new moving metal surfaces for proper surface mate qualities. The same mech stated that he recommends waiting 5000-6000 miles before switching to any syn type oil. I have not called Comp Cams but it sounds like they would sort of say the same thing. I've got 4200 miles on the 04 have had 3 oil & filter changes. At 100 miles changed oil and filter and switched to mag drain plug. Changed again at 1500 miles and the mag drain plug was loaded with metal stuff, changed again at 3200 mag drain plug was mostly clean. I will change again at 6000 miles, have not decided if I will stick with reg Valvoline or go syn. Safe driving to all !!!